1. Field of the Invention
The present invention relates to a portable device. More particularly, the present invention relates to an apparatus and a method for displaying capacity and a charge/discharge state in a portable device.
2. Description of the Related Art
Portable devices such as mobile phones are supplied with power from a battery in which a rechargeable battery is often used. The rechargeable battery has to be recharged at a proper time before becoming completely dead. For doing so, the portable devices provide a function which displays a current battery capacity to inform a user of a recharge time.
Conventional methods for determining and displaying the battery capacity are described below.
The most basic method for determining and displaying the battery capacity is a voltage measurement method. The voltage measurement method determines and displays the battery capacity by comparing a battery voltage with a discharge table that is based on the fact that the battery voltage decreases according to the discharge state of the battery. The voltage measurement method is implemented in terms of hardware with low cost due to small modules being used. However, the voltage measurement method may display an incorrect capacity because of a temporary increase or decrease of battery voltage due to a load of the device that is supplied from the battery and a reference voltage for displaying the remaining capacity is changed or fluctuated.
A Coulomb counting method determines the battery capacity by storing and accumulating an electric charge transported between the battery and the device, to a memory, and displays the remaining battery capacity. This method features easy software implementation and high accuracy. However, the Coulomb counting method includes high cost because an additional memory is required and the hardware is more complicated than the voltage measurement. Also, the Coulomb counting method includes a smaller capacity than a same-size battery because the information depends on the single battery and a measurement Integrated Circuit (IC) is to be installed to the battery. In comparison to the voltage measurement method, the voltage fluctuation is not a problem. However, when the accumulated data is shifted once after several charges and discharges, data is unreliable. Thus, it is necessary to reset the capacity by completely recharging or discharging the battery.
A voltage measurement compensation method, which is an enhanced version of the voltage measurement method, measures the voltage between the battery and a resistance by placing a sensing resistance between the battery and the device. The voltage measurement compensation method estimates and compensates for the current value using a difference between the resistance and the voltage based on a determined battery capacity value. Disadvantageously, the voltage measurement compensation method suffers from a low voltage supplied to the device due to the use of the sensing resistance and the increased battery consumption.
Therefore, a need exists for an efficient method for measuring a battery capacity and informing of a charge state or a discharge state.